# Inductor - Definition, Types of Inductors, Formula, Functions, Working Principle (2023)

Inductors much like conductors and resistors are simple components that are used in electronic devices to carry out specific functions. Normally, inductors are coil-like structures that are found in electronic circuits. The coil is an insulated wire that is looped around the central core.

Inductors are mostly used to decrease or control the electric spikes by storing energy temporarily in an electromagnetic field and then releasing it back into the circuit.

## What is Inductor?

An inductor is a passive component that is used in most power electronic circuits to store energy in the form of magnetic energy when electricity is applied to it. One of the key properties of an inductor is that it impedes or opposes any change in the amount of current flowing through it. Whenever the current across the inductor changes it either acquires charge or loses the charge in order to equalize the current passing through it. The inductor is also called a choke, reactor or just coil.

An inductor is described by its distinctive nature of inductance, which is defined as the ratio of the voltage to the rate of change of current. Inductance is a result of the induced magnetic field on the coil. It is also determined by several factors such as;

• The shape of the coil.
• The number of turns and layers of the wire.
• The space that is given between the turns.
• Permeability of the core material.
• The size of the core.

The S.I. unit of inductance is henry (H) and when we measure magnetic circuits it is equivalent to weber/ampere. It is denoted by the symbol L.

Meanwhile, an inductor is totally different from a capacitor. In the case of a capacitor, it stores energy as electrical energy but as mentioned above, an inductor stores energy in the form of magnetic energy. One key feature of the inductor is that it also changes its polarity while discharging. In this way polarity during discharging can be made opposite to the polarity during charging. The polarity of the induced voltage is well explained by Lenz law.

Symbols for an inductor are given below:

## Construction of an Inductor

If we look at the construction of an inductor it usually consists of a coil of conducting material (widely used ones include insulated copper wire) that is wrapped around a core that is made up of plastic material or ferromagnetic material. One advantage of using a ferromagnetic core is that it has high permeability which helps in increasing the magnetic field and at the same time confining it closely to the inductor. Ultimately this results in higher inductance.

On the other hand, inductors with low frequency are usually constructed like transformers. They have cores made up of electrical steel that is laminated to help prevent eddy currents. ‘Soft’ ferrites are also widely used for cores above audio frequencies.

Inductors do come in many shapes and types. In some inductors, you will find an adjustable core that allows changing the inductance. Inductors that are used in blocking very high frequencies are mostly made by stringing a ferrite bead on a wire.

Planar inductors are made using a planar core while small value inductors are built on integrated circuits using the processes of making interconnects. Typically, an aluminium interconnect is used and fixed in a spiral coil pattern. However, small dimensions have some limitations. They restrict the inductance.

There are also shielded inductors which are commonly used in power regulation systems, lighting, and other systems requiring low-noise operating conditions. These inductors are often partially or fully shielded.

## Different Types of Inductors

Depending on the type of material used inductors can be classified as follows:

1. Iron Core Inductor
2. Air Core Inductor
3. Iron Powder Inductor
4. Ferrite Core Inductor which is divided into,
• Soft Ferrite
• Hard Ferrite

### Iron Core Inductor

As the name suggests the core of this type of inductor is made of iron. These inductors are low space inductors that have high power and high inductance value. However, they are limited in high-frequency capacity. These inductors are used in audio equipment.

### Air Core Inductor

These inductors are used when the amount of inductance required is low. Since there is no core, it does not have a core loss. But the number of turns the inductor must have is more for this type when compared to the inductors with the core. This results in a high-Quality factor. Usually, ceramic inductors are often referred to as air-core inductors.

### Iron Powder Inductor

In this type of inductor, the core is Iron Oxide. They are formed by very fine and insulating particles of pure iron powder. High magnetic flux can be stored in it due to the air gap. The permeability of the core of this type of inductor is very less. They are usually below 100. They are mainly used in switching power supplies.

### Ferrite Core Inductor

In this type of Inductor, ferrite materials are used as core. The general composition of ferrites is XFe2O4. Where X represents transition material. Ferrites can be classified into two types. Soft ferrites and hard ferrites.

• Soft Ferrite: Materials that have the ability to reverse their polarity without any external energy.
• Hard Ferrite: These are permanent magnets. That is their polarity will not change even when the magnetic field is removed.

### Choke

A choke is a type of inductor that is used mainly for blocking high-frequency alternating current (AC) in an electrical circuit. On the other hand, it will allow DC or low-frequency signals to pass. As the function of this inductor is to restrict the changes in current it is called a choke. This inductor consists of a coil of insulated wire wound on a magnetic core. The main difference between chokes and other inductors is that in their cases they do not require high Q factor construction techniques meant to reduce the resistance in inductors found in tuned circuits.

## Functions of an Inductor

Inductors can be used for two primary functions.

1. To control signals.
2. To store energy.

### Controlling Signals

Coils in an inductor can be used to store energy. The function of the inductor depends upon the frequency of the current passing through it. That is for higher frequency signals will be passed less easily and vice versa. This function tells that it blocks AC Current and passes DC Current. Hence, it can be used to block AC signals.

Inductors can be used along with capacitors to form LC filters.

### Storing Energy

Inductor stores energy in the form of magnetic energy. Coils can store electrical energy in a form of magnetic energy using the property that an electric current flowing through a coil produces a magnetic field, which in turn produces an electric current. In other words, coils offer a means of storing energy on the basis of inductivity

## Inductors In Parallel Form

If two terminals of an inductor are connected to two terminals of another inductor, then the inductors are said to be parallel. We know that when resistors are connected in parallel, their effective resistance decreases. Similarly, when inductors are connected in parallel form, their effective inductance decreases. Inductors in parallel are somewhat similar to the capacitors in series.

Consider the example below:

Here, the current flowing through each inductor will be different. This current depends upon the inductance value. However, the voltage across each conductor will be the same. By using Kirchoff’s Current law total current is the sum of the current through each branch. That is

IT = I1 + I2 +I3

We know that the voltage across an inductor is given by the equation

V = L di / dt

We can write,

vAB = LTotal x dlt / dt

VAB = LTotal x d (I1 + I2 + I3) / dt

We can further write it as

vAB = LTotal x dl1 / dt + LTotal x dl2 / dt + LTotal x dl3 / dt

That is

vAB = LTotal ( V / L1 + V / L2 + V / L3 )

Since voltage are equal we can simplify the equation as,

1 / LTotal = 1 / L1 + 1 / L2 + 1 / L3

## Inductors In Series

When the inductors are chained together in a straight line or when they are connected end to end, then the inductors are said to be in series connection. We know that when resistors are connected in series, their effective resistance increases.

Similarly, when inductors are connected in series, their effective inductance increases. Inductors in series are somewhat similar to the capacitors in parallel. In Order to get the total inductance, it is very easy. You only have to add every inductance. That is when inductors are connected in series, the total inductance is the sum of all inductance.

Consider the connection below :

Here three inductors, and are connected in series. In this case, the current flowing through each inductor is the same while the voltage across each inductor is different. This voltage depends upon the inductance value. By using Kirchoff’s voltage law total voltage drop is the sum of the voltage drop across each inductor. That is

VT = V1 + V2 +V3

We know that the voltage across an inductor is given by the equation

V = L di / dt

So here we can write,

LTotal dl / dt = L1 x dl1 / dt + L2 x dl2 / dt + L3 x dl3 / dt

But

I = I1 = I2 = I3

Therefore,

L dl / dt = L1 x dl / dt + L2 x dl / dt + L3 x dl / dt

LTotal = L1 + L2 + L3

## Energy Stored In An Inductor

When a current passes through an inductor an emf is induced in it. This back emf opposes the flow of current through the inductor. So in order to establish a current in the inductor work has to be done against this emf by the voltage source.

Consider a time interval dt.

During this period, work done dW is given by

dW = Pdt = – Eidt = iL di / dt x dt = Lidi

To find the total work done the above expression must be integrated.

W = 0ILidi = ½ LI2

Therefore energy stored in an inductor is given by the equation,

W = ½ LI2

## Impedance of an Inductor

AC resistance mostly determines the opposition of current flowing through a coil. This AC resistance is most commonly known as impedance. In this section, since we are discussing the opposition given by the inductor, this can be called as Inductive Reactance. Inductive reactance which is given the symbol XL is the property in an AC circuit that opposes the change in the current.

It is given by the equation,

XL = VL / IL = Lω

From the equation, it is clear that inductive reactance is proportional to frequency.

The plot of frequency vs reactance is given below:

## Frequently Asked Questions on Inductor

### What is the value of the power factor for a pure inductor?

For a pure inductor, the power factor is zero.

### What is self-induction?

The phenomenon in which an emf is induced in a coil due to the change of current through the coil itself is known as self-induction.

### What is mutual induction?

The phenomenon in which a change of current in one coil induces an emf in another neighbouring coil is called mutual induction.

### When is emf induced in a circuit?

An emf is induced in a circuit whenever there is a change in the magnetic flux passing through it.

## FAQs

### What is inductor and working principle? ›

An inductor is a passive electronic component which is capable of storing electrical energy in the form of magnetic energy. Basically, it uses a conductor that is wound into a coil, and when electricity flows into the coil from the left to the right, this will generate a magnetic field in the clockwise direction.

What is inductor and its formula? ›

Inductor Unit

The magnetic flux fluctuates as a result, and an electromotive force is induced. L is the symbol for inductance formula, and Henry is the inductor unit of measurement. The induced one volt by altering current in one ampere per second in an inductance value is equal to one Henry value. L=μN2Al.

What is inductor and types of inductor? ›

An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil. Inductor. A selection of low-value inductors. Type.

What is the function of inductor? ›

An inductor has the functions of developing electromotive force in the direction that reduces fluctuation when a fluctuating current flows and storing electric energy as magnetic energy.

What is the definition of an inductor? ›

An inductor is a passive electrical component that opposes sudden changes in current. Inductors are also known as coils or chokes. The electrical symbol for an inductor is L.

What is the formula of induction? ›

It is also known as electromagnetic induction. The magnetic induction formula is given as ϵ=dϕbdt ϵ = d ϕ b d t .

What is the most common inductor? ›

The commonly seen inductor, with a simple winding is this air-Core Inductor. This has nothing but air as the core material. The non-magnetic materials like plastic and ceramic are also used as core materials and they also come under this air-core Inductors. The following image shows various air-core inductors.

What is the unit of inductor? ›

The standard unit of inductance is the henry (H). Because the henry is such a large unit, many inductors are measured in smaller quantities, such as the millihenry, abbreviated mH (1 mH equals 10-3 H), and the microhenry, abbreviated µH (1 µH equals 10-6 H).

What is the unit symbol of inductor? ›

The henry (symbol: H) is the unit of electrical inductance in the International System of Units (SI). If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self inductance of 1 henry.

What is the formula of inductor voltage? ›

V = L × (di/dt)

V = Voltage (volts), L = Value of Inductance (H), i = Current (A), t = Time taken (s).

### What is the formula of inductor coil? ›

The amount of self-induced back-emf produced depends upon how fast the magnetic field is changing, and thus upon how fast the current through the coil is changing which is proportional to frequency. Defining the equation for an inductor as being VL = L(di/dt).

What is the main property of an inductor? ›

Inductors have the following basic characteristics. Current flows to generate a magnetic field, and a change of the magnetic field generates an opposing current. Changes electrical energy to magnetic energy and stores it. DC can pass through but AC cannot easily pass through at higher frequencies.

What is the first principle of induction? ›

The principle of mathematical induction is then: If the integer 0 belongs to the class F and F is hereditary, every nonnegative integer belongs to F. Alternatively, if the integer 1 belongs to the class F and F is hereditary, then every positive integer belongs to F.

What are the two types of induction? ›

Induction motors are categorized into two main types: single-phase and three-phase induction motors. And there are further classifications based on their way of starting. The single-phase induction motor is not self-starting.

What causes an inductor to fail? ›

Inductors often fail open due to corrosion or bad internal solder joints or the inductors fail shorted due to electrical overstress, bad magnet wire insulation, or potting issues. Some images of common inductor failures are shown below.

What devices use inductors? ›

Based on the requirement, inductors have many applications in electrical transmission.
• Inductors in Tuned Circuits.
• Inductive sensors. Energy Storage Devices.
• Induction Motors.
• Transformers.
• Inductive Filters.
• Chokes.
• Ferrite beds.
• Relays.
Sep 5, 2015

What happens when inductor is connected to AC? ›

An inductor can oppose or block the passage of alternating current through it. The inductor either acquires the charge or loses the charge. The current across the inductor changes to equalize the current passing through it.

Are inductors ac or DC? ›

The main action of an inductor is to resist a change in current. However, since the current in a DC circuit is constant, there is no induced voltage developed instantaneously across the inductor.
...
Inductors in a DC Circuit Example.
Number of Time ConstantsApproximate % of Initial Current
51 (considered 0%)
4 more rows

What is the energy of inductor? ›

An inductor carrying current is analogous to a mass having velocity. So, just like a moving mass has kinetic energy = 1/2 mv^2, a coil carrying current stores energy in its magnetic field giving by 1/2 Li^2.

What is Ohm's law for inductor? ›

Since the voltage drop across the resistor, VR is equal to I*R (Ohms Law), it will have the same exponential growth and shape as the current. However, the voltage drop across the inductor, VL will have a value equal to: Ve(-Rt/L).

### What is this power factor? ›

Power factor is the relationship (phase) of current and voltage in AC electrical distribution systems. Under ideal conditions current and voltage are “in phase” and the power factor is “100%.” If inductive loads (motors) are present, power factor less than 100% (typically 80 to 90% can occur).

What are the basics of inductor? ›

The basic structure of an inductor consists of a conductive wire wound in a coil shape and is able to convert electric energy to magnetic energy and store it inside the inductor. The storable amount of magnetic energy is determined by the inductance of the inductor and measured in Henry (H).

How do inductors work in a circuit? ›

Inductors are typically used as energy storage devices in switched-mode power devices to produce DC current. The inductor, which stores energy, supplies energy to the circuit to maintain current flow during “off” switching periods, thus enabling topographies where output voltage exceeds input voltage.

What is the difference between an inductor and a capacitor? ›

One of the main differences between a capacitor and an inductor is that a capacitor opposes a change in voltage while an inductor opposes a change in the current. Furthermore, the inductor stores energy in the form of a magnetic field, and the capacitor stores energy in the form of an electric field.

What is the purpose of inductor and capacitor? ›

Capacitors and inductors are electronic components that can store energy supplied by a voltage source. A capacitor stores energy in an electric field; an inductor stores energy in a magnetic field.

Does inductor work on AC or DC? ›

Resistors can be used in both AC and DC circuits whereas inductors can only be used in DC circuit.

What does an inductor do to voltage? ›

The inductor, always opposing any change in current, will produce a voltage drop opposite to the change's direction. With that in mind, how much voltage the inductor will produce depends on how rapidly the current through it is decreased.

How do you identify an inductor? ›

Surface mount inductors or chip inductors use color dots instead of color bands. There are generally three dots that are read clockwise from the top. The first two dots indicate the significant digits of the inductance value, and the third dot indicates the multiplier. The value of inductance is obtained in Nano Henry.

## References

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